Primary Quench Detection Analysis for the EU-DEMO Toroidal Field Coils

To protect the Toroidal Field Coils (TFC) of the EU DEMO tokamak, in case it will be realized with low temperature superconducting (LTS) materials, a reliable and fast quench detection system (QDS) is required. Although these TFC coils are operated in static mode, voltages across their winding pack (WP) will be generated during machine operation due to the presence of dynamic magnetic fields. Two sources of magnetic coupling, responsible for noisy signals on the quench detection circuitry in a Fast Plasma Disruption scenario, are here considered and analyzed. Due to the high electromagnetic noise environment, the co-wound (CW) technology must be adopted for the quench sensors and an aligned and twisted layout (CWA&T) is necessary due to the magnetic interaction with the superconductor (SC) strand helicity. The poloidal component of the plasma current is responsible for a noisy signal on the CW and a strategy for signal compensation will be suggested and the contribution evaluated numerically. The signal induced on a SC cable due to the helicity can be compensated adopting a CWA&T configuration. The twist pitch length (TP) of the CWA&T is a critical parameter for a proper noise compensation. Since it is challenging to obtain a reliable TP length from a numerical simulation, we here propose an experimental approach to assess the proper TP length. There is not a constraint on the TP length from the poloidal plasma current induced signal and we can conclude that a single TP, optimized for helicity compensation, will be sufficient.